1. Field of the Invention
This invention relates to paperboard composite structures incorporating a silicon-oxide ("glass")-coated film. Structures of this type generally improve the shelf life of refrigerated juices and other oxygen-sensitive products and provide a barrier to flavors and fragrances to maintain product quality.
2. Description of the Related Art
One criterion for determining the end of the shelf life of refrigerated juices and other oxygen-sensitive products is the Vitamin C content of the product. Because Vitamin C is easily oxidized, the oxygen barrier of the carton is one predictor of shelf life. Studies have shown that carton barrier is a function of the oxygen permeability of the laminate and of the "leakage" through the seals and seams of the carton.
It is known that currently available cartons with ethylene-vinyl alcohol (EVOH) or nylon as the barrier layer, formed and filled on standard filling lines, provide about eight weeks of shelf life for orange juice. However, it is well known that EVOH is sensitive to humidity and loses much of its oxygen barrier at high humidity which is typical of the refrigerated storage of liquids. Also, EVOH is sensitive to sealing temperatures and has a relatively narrow window of sealability.
It is also known to use aluminum foil in barrier packaging. While aluminum foil is an excellent barrier, it is expensive and makes recycling or incineration of the used containers more difficult.
Finally, the use of gable top cartons incorporating glass-coated film, instead of aluminum foil barriers has been developed, as set forth in an article entitled "SiOx coating ups shelf life", Packaging Digest.RTM., dated December 1995. The glass-coated film is located between plies of polyethylene (PE) on the outside of the paperboard cartons. The paperboard cartons employ an inner lining of PE. While these cartons employ the advantageous silicon oxide layer, the silicon oxide layer must be located as close to the food product as possible in order to best retain the Vitamin C within the product and, thus, increase the shelf life of the food product within the container. Therefore, a more advantageous container will be presented if the glass-coated film were located as close as possible to the food product located within the container.
It is also known in U.S. Pat. No. 5,296,070 ('070), to Take et al., entitled "Process For Producing Liquid Container Material," that the resins which contact the glass coating need to be cooled to below 194.degree. F. (90.degree. C.) and preferably below 122.degree. F. (50.degree. C.) in order to avoid cracking.
It is apparent from the above that there exists a need in the art for a paperboard container which is economical to construct, but which at the same time substantially increases the shelf life of the food product contained within the container. It is the purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.